What is the major hormone that influences metabolism and the immune response?

The major hormone influencing metabolism and immune response is Cortisol.

Cortisol is a steroid hormone and belongs to glucocorticoid class of hormones. The release of substances causing inflammation is prevented by cortisol.

The immune system activity is weakened by the cortisol. The action of cortisol results in shifting towards the Th2 immune response in contrast to general immunosuppression.

The proliferation of T-cells is prevented by rendering the interleukin-2 producers T-cells and is unresponsive to interleukin-1 and T-cell growth factor (IL-2) and is unable to produce it. The natural killer cells get affected by the cortisol.